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Q.
The number of $3$ digit numbers having at least one of their digit as $5$ are
Permutations and Combinations
Solution:
Total number of $3$ - digit numbers having at least one of their digits as $5=$ Total number of $3$ -digit numbers
- (Total number of $3$ - digit numbers in which $5$ does not appear at all $)=9 \times 10 \times 10-8 \times 9 \times 9$
$=900-648=252$